Various methods have been proposed by the prior art for the production of sulfones. The best known prior art processes for producing sulfones is probably the reaction of two moles of phenol with one mole of sulfuric acid to form a sulfone compound and water. Unfortunately, a major drawback to this method is that a substantial amount (10-29%) of the 2,4'-isomer by-product, instead of the desired 4,4'-isomer product, is provided when the above process is employed. And, since the removal of the 2,4'-isomer from the product mixture is difficult, additional losses of 4,4'-isomer result during purification. Therefore, the final yield of product is relatively low. Furthermore, dark-colored impurities and tars are formed which are also difficult to eliminate. Finally, the disposal of both of the above impurities provides ecological problems to the manufacturer.
U.S. Pat. No. 3,297,766 to Bradley et al.; 3,318,956 to Mausner; 3,366,692 to Orem; and 3,383,421 to Fox et al., describe various schemes to produce a high-purity sulfone employing the above phenol-sulfuric acid reaction.
Another process is U.S. Pat. No. 3,699,171 to Sanderson et al., which provides a process employing nitrogen oxide in the presence of sulfuric acid and a molecular oxygen to produce an aryl alkyl sulfone from an aryl alkyl sulfoxide. Moreover, U.S. Pat. Nos. 2,793,234 to Metivier; 3,019,266 to Buc et al.; 3,069,471 to Tashlick; 3,118,952 to Crowther et al., all provide methods employing peroxide to oxidize alkyl or dialkyl sulfides and/or sulfoxides to their corresponding sulfone compounds.
In U.S. Pat. No. 3,449,439 to Kuhnen et al., a sulfone is produced from an organic sulfide, or organic sulfoxide, by reacting same with an organic hydroperoxide in the presence of a metallic catalyst compound of titanium, molybdenum, or vanadium.
Three patents assigned to General Aniline and Film Corporation, U.S. Pat. Nos. 3,005,852 to Freyermuth; 3,006,962 to Schultz et al.; and 3,006,963 to Buc et al., describe the production of sulfoxides and sulfones by an oxidation process employing as a catalyst system hydrogen peroxide and a molybdenum, vanadium, or tungsten catalyst. In each case, a two-stage reaction sequence is provided. In stage one, the sulfide is oxidized to sulfoxide, while in the second stage, the sulfoxide is converted oxidatively to the sulfone. "Cooling is often required to prevent the temperature from rising to a point detrimental to the reaction or to the chemical structure of the intermediate and final compound." (see U.S. Pat. No. 3,005,852, page 2, column 3).
For instance, in the Freyermuth et al. patent, a molybdenum-peroxide catalyst is provided to oxidize a dialkyl sulfide compound. More specifically, the dialkyl compound comprises a single aromatic ring structure attached to the terminal alkyl group of at least one pendant constituent having a structure in which a divalent sulfur atom is attached to a pair of alkyl groups. The compound, for purpose of the sulfide oxidation, acts as a dialkyl, not a diaryl, sulfide. The broad pH range over which the subject reaction is supposedly viable is from about one to about 10 to 11, preferably pH range being from 5 to 7. It is noted, however, that all of the reactions shown in the examples in this application are run at a pH of 5 to 6.
Next, in the Schultz et al. patent, the vanadium-peroxide catalyst is employed to oxidize a reactant compound containing at least one divalent sulfur atom bonded to two carbon atoms, although no diaryl sulfide reactants are shown in the examples. The broadest pH range in this case is from 0.5 to 6, the preferable range being from about 1 to 3.
Finally, the Buc et al. patent presents a tungsten-peroxide oxidation system in which a divalent sulfur atom bonded to two carbon atoms is reacted to form a sulfoxide or a sulfone, the pH range being from about one to 10 or 11, and preferably from about 6 to 7.
It is quite clear from reviewing the above patents that different reactants at different pH levels are provided in each of the various catalyst systems employed in each of the three patents set forth. Accordingly, the above differences among oxidation catalyst systems preclude extrapolation of the reaction parameters outlined for a given catalyst with respect to another catalyst. Instead, the differences limit each reaction system to include only the reactants and process conditions which they particularly disclose and specify. As an illustration in support of the proposition that each of the above GAF patents is self-limiting, an article in the Journal of Organic Chemistry, Volume 28, pages 1140-1142, (1963), the above patentees, i.e., Freyermuth, Schultz and Buc, have co-authored an article entitled "New Catalysts for the Oxidation of Sulfides to Sulfones with Hydrogen Peroxide". On page 1141 of the above article, the authors state, in the first sentence of column 1, paragraph 2, that "The vanadium catalyst is satisfactory only in the pH range 1-2." Furthermore, in the first sentence of column 1, paragraph 3, statement is made that "Tungsten and molybdenum catalysts are operable over a broader pH range than the vanadium catalyst. The preferred pH is about 5-6, but satisfactory reactions have been carried out at about pH 3-8."
Finally, an article entitled "Catalysts for the Hydrogen Peroxide Oxidation of Sulfides to Sulfones", by N. W. Connon, Eastman Organic Chemical Bulletin, Volume 44, No. 1 (1972), provides a review of the prior art including a number of the references cited above. The Eastman bulletin discloses the oxidation of water-soluble di-aliphatic sulfides, employing molybdate salts as catalysts for the hydrogen peroxide in that oxidation.